Automatic tuning apparatus



ec. 25, 1945. R. W, MAY 2391,47@

AUTOMATI C TUNING APPARATUS Filed May 1'7, 1945 4 Sheets-Sheet l zz J4@a ji' j l A x9 rf r//l/f/l/g/ 6,/

Rw. MAY 2,3%479 y Dec. 25, 1945.

4 She Dec. 25, 1945. R, W MAY 2,391,470

AUTOMATIC TUNING APPARATUS Filed May 17, 1943 4 Sheets-Sheet 3 awa 'f/zdf/fz Dec. 25, 1945. R W MAY AUTOMATIC TUNING APPARATUS Filed May 17,1945 4 Sheets-Sheet 4 @ZW/ 6 Si Patented Dee. 25, 194s NTED ST RichardW. May, Cedar E Collins Radio Company,

Application May lll, 1949, Serial No. 487,395

(tCl. Ri-T142) ll Claims.

This invention relates to automatic tuning ap paratus for positioning ashaft at a desired point in any of a plurality of revolutions, and moreparticularly to a limit switch particularly designed for such tuningapparatus.

One feature of this invention is that it enables, without mechanicaldiiliculties, proper electrical limit control of automatic tuning meansfor use with a radio tuning shaft rotatable through a plurality of.revolutions; another feature of this invention is that rotation of thelimit switch shaft may continue, after operation of the switch means,for as long as may be desirable without jamming of the operating parts;lstill another feature of this invention is that the actuating mem-u berfor actuating the switch means is driven by a shaft rotatable through alarge number of revolutions, preferably similar to the rotation of thetpned shaft; and yet another feature of this invention is that theactuating member 'is rotatably mounted on a nut on the limit switchthreaded shaft with readily adjustable frictional engagement. Otherfeatures and advantages of this invention will be apparent from thefollowing speciication and the drawings, in which:

Figure l is a schematic diagram of apparatus embodying my invention,with the parts in one terminal position; Figure 2 is a schematic diagramof one portion of that shown in Figure 1, but in. a different position;Figure 3 is a schematic diagram similar to Figure 2, but with the partsin still another position; Figure 4 is a schematic diagram similar toFigure 3, but with the parts in still a different position; Figure 5 isa side elevation of a shaft positioning unit adapted to automaticallyposition a shaft at any desired point throughout a range of a pluralityof revolutions, hereafter termed a multi-turn" unit; Figure 6 is atransverse sectional view of the slip clutch, along the line 6 6 ofFigure 5; Figure 7 is a. sectional vlew of the multi-turn unit, alongthe line l-l of Figure 5, with a portion of the limit switch actuatingmember broken away; Figure 8 is an elevational view, partly in section,of the ratchet and one end of the selector cam assembly; Figure 9 is afragmentary enlarged side elevational view of the limit switch, with themoving parts being shown in solid lines at one limit of their movementand in dotted lines at the other limit; Figure 10 is a view along theline lll-l0 of Figure 9,v partially broken away; and Figure 11 is awiring diagram of a circuit adapted to operate the particular embodimentof my invention shown.

The multi-turn shaft positioning unit disclosed in this application isan improvement on auto- I liti apids, iowa, assigner to a corporation oiHowe.

matic tuning apparatus mechanically positioning the' shaft of a tunedelement automatically as the result of a sequence of operationsinitiated by movement of a control switch. Apparatus oi this generaltype has been the subject of a number of patents issued to one Arthur A.Collins, one of the more recent of these patents being No. 2,285,414,issued June 9, 1942.

The automatic tuning arrangements which are the subject of such previouspatents were all designed for and operable only in connection with ashaft designed to be rotated through an arc not exceeding onerevolution, suilcient for the tuning of elements such as a conventionalcondenser, 'tap switch, or the like. Certain elements of a radio set,however, can be better tuned by a shaft rotat able through a pluralityof revolutions.. example, a permeability tuning core is preferably movedin or out of its cooperating coil by rotation of a threaded lead screwwhich may rotate through twenty turns to vary the inductance fromminimum to maximum; and certain types of condensers and carbon pileresistors are preferably driven by lead screws.

The said Arthur A. Collins has recently developed a multi-turn shaftpositioning unit and associated operative mechanism and control circuitcapable of rotating the shaft of a tuned element through any number ofdesired revolutions and of stopping the shaft automatically with a highdegree of accuracy at any desired point in the entire range of movement.The general principles and major combination of elements of a multi-turnunit, and some of the detailed improvements thereof, have been inventedby the said Arthur A. Collins and are the subject matter of hisco-pending applications, Serial No. 472,717, led January 18, 1943, andSerial No. 483,899, led April 21, 1943. Certain other speciiic portionsof a multiturn unit have been improved by me. An improved limit switchspecilcally designed for such an automatic tuning device is the subjectof this application; and certain other features are covered by my otherco-pending applications, Serial For l No. 515,250, led December 22,1943, and Serial l of switch to select similar stop combinations in\ allof the units, whereupon the various circuit elements would be instantlyand automatically tuned to thedesired .predetermined frequency. Forsimplicity of explanation only a multi-turn unit is shown here, but itwill be understood that this can be used in combination with single turnunits of the kind previously shown in issued patents or of the kindshown in the aforesaid Collins application, Serial No. 472,717.

In the particular embodiment of the invention illustrated here, .andreferring now more particularly to Figure 1, the schematic diagram, areversible electric motor 20 drives a main shaft 2i which in turndrivesa cross shaft or line shaft tional line shafts may be provided.

The main shaft of the multi-turn unit is the rotatable shaft 24 whichoperates through a lead screw arrangement to move a permeability core ortuning slug 25 axially of a coil 26, this core being so mounted (as by asplinedarrangement not shown) as to enable axial movement whilepreventing rotational movement thereof. Mounted on a drum on the shaft24 in a manner to be hereafter more fully described (normallynon-rotatable with respect to the shaft) are a plurality of tuning stoprings 21, a' manual stop ring 28 (which may be part of the vstop meanson the stop ring mounting drum), and a terminal stop ring 29. While allof these are non-rotatably locked to the shaft 24 during operation, thetuning stop rings 2l may be unlocked to permit setting or vpre-selectionof the point at which the shaft is to stop. A worm on the line shaft 22drives a worm gear 3l (as at a 121/2 to 1 ratio, for example), the wormgear driving one of the two elements of a slip-clutch 32,l the otherelement of this clutch being connected to and driving the shaft 24.

The worm gear 3i also drives a limit switch, lhere indicated in generalas 33, through a slipclutch arrangement indicated as 80. A threadedshaft 8l carries an operating arm 82, this being shown in the terminalposition of a cycle of operation, with the movable contact 83 out of engagement with the contact 84. Upon initiation of a cycle of operation bymanipulation of the selector switch to call for a new frequency setting,the operating arm 82 travels to the left (83 iirst engaging 84 andmoving it out of engagement with 85) until contact between 86 and 8l isbroken, the motor thereafter reversing as will be more fully describedlater in connection with the circuit diagram (Figure 11), whereupon thelimit switch arm reverses and travelsback to its terminal position shownin Figure 1 of the drawings.

Another worm 34 on the line shaft 22 drives a worm gear 35 (as at a 40to 1 ratio), this in turn acting through a single-tooth ratchet, hereindicated in general as 36, to drive (in one direction only) a shaft 31.This shaft has non-rotatably mounted thereon a plurality of tuningselector cams 38, a manual selector cam 33, and a terminal stop ring(which may be part 'of the cam drum). Another shaft 4I carries aplurality of ,22. This one line shaftmay drive a number ofseparate'tuning units simultaneously,lor addithe shaft 4|. but thesecondary cams are mounted with a frictional retention su-ch that theynormally move with the shaft, but can slip if the frictional force isexceeded. The shaft 4i is driven from the shaft 24 in fixed relationthereto.

by gearing, here indicated in general as 45, appropriateto the number ofturnsl for which the unit is designed, as for example with a gear ratioof 23% to 1.

A stud 48 provides a mounting for a plurality of automatic tuning pawls4l, a manual tuning pawl 48, and a terminal stop pawl 49. The pawls 4land 48 are biased in one direction by the rod springs 60 and 5I, whilethe terminal stop pawl 491s normally biased to a position intermediatethe full line and dotted line positions by a coil spring 52.

Referring first to the terminal position pawl,

all of the parts are shown at one terminal, where 'ure 1), while thering 44 would begina corresponding clockwise rotation at a greatlyreduced rate. As soon as this latter ring moved a, few degrees theterminal stop pawl 49 would be permitted to assume an intermediateposition under the influence of the spring 52, and the shaft 24 would befree to rotate through a desired number of revolutions (as a little overtwenty revolutions) until the shoulder 44a had come around to its dottedline position and forced the terminal stop pawl 49 to its dotted lineposition, whereupon the shoulder 29a would engage one of the ends ofthis stop pawl and stop the tuned shaft at its other terminal position,hereafter designated the "home position. Then as soon as the sequence ofloperations. effected reversal of the motor 20 the shaft 24 and itsassociated rings would begin to rotate in the reverse or clockwisedirection, being free to rotate in this direction until stopped -by oneof the tuning stop combinations or by the terminal stop arrangement asillustrated in solid v lines.

When automatic tuning is eiected by the sequence of operations to behereafter more fully described, one step is the selection of the tuningpawl 4l which is to be rendered operative. This is accomplished byrotating the selector cam drum until the slot 38a lies immediately underthe portion 41a of the pawl, the pawl then moving slightly (under theinuence of the spring 50) until the end 41h drops down onto theperiphery of the secondary cam 42, this position 'of the partsthen'continues rotation (in a clockwise direction,

secondary or turn determining cams 42, a. sec- 44. This latter cam isimmovably mounted on speaking with respect to these views) until the end41e of .the pawl drops into the slot 21a and strikes whatmay be termedthe forward shoul- 'der 21h of this slot, this situation beingillustrated-'in Figure 4. This stops rotation of the shaft 24 although,because of slippage in thev clutch 32, the line shafts and other unitsmay continue until the cycle of operation is terminated.

It will thus be seen that a desired number ofautomatic stop combinationsmay be provided, each being a duplicate of the combination justdescribed. Each. such combination includes means for selecting thatcombination, one of the selector cams; means for determining in whichturn or revolution of the shaft 24 the pawl will be permitted to moveinto operative relationship with the stop ring 21, this means comprisingthe secondary cam 42; and means for stopping the shaft of the tunedelement at a desired point in the chosen revolution, this being effectedby engagement of the end of the pawl with the forward shoulder of theslot of the stop ring 21. The shafts 24 and 4I, and thus the stop ringsand secondary cams, are maintained in synchronizatlon and moved inappropriate ratios to each other by the interconnecting gear train 4l,so that whenever a given stop combination is selected the shaft of thetuned element will be stopped very accurately and precisely at thechosen point in the chosen revolution, which point may be anywherethrough a full range of continuous rotation of the shaft 24.

While the full sequence cf operations of an automatic tuning cycle willbe explained in detail later in connection with the description of thevarious switches and relays effecting such sequence, itis believed thatunderstanding of the present invention will be facilitated by a briefdescription of a tuning operation at this time. When it is desired tochange the transmitter to a different predetermined frequency theoperator turns a control switch to the corresponding setting, whereuponthe motor 20 starts to rotate in a direction moving all of the partstoward home position. The motor rotates through a predetermined numberof turns determined by the limit switch, various tuned shafts reachinghome position at various times (depending on their previous positions)and their respective clutches thereafter slipping. When this portion ofthe cycle is completed the motor continues operation in the samedirection ("beyond home, as it might be termed) being stopped somewhereduring this additional rotation by an automatic selector switch,stoppage of the motor occurring when the selector cam arrangements arein such position as to actuate the desired stop combination, the onecorresponding to the control switch setting. Thereupon the motorreversesand drives the parts in the tuning direction (but withoutdisturbing the selector cams), the various units rotating in thisdirection until each tuned shaft is stopped by the selected pawl at aposition appropriate to the frequency desired, the respective clutchesthereafter slipping until the motor and lines shafts have completed thefull cycle and have been stopped by the limit switch.

In order to effect selection of the desired stop combination the shaft31 rotates, through a lost motion connection comprising the parts 60 and6I, the rotatable portion 82a of an automatic selector switch or circuitseeking switch 62. This switch comprises a plurality of fixed taps orcontacts 63a-l and a rotatable member adapted to make contact with allof the taps except one which lies within the confines of a slot in thisrotatable member. While the unit illustrated here is shown as havingboth a limit switch and a selector switch, in order that an operableunit may be shown, it will be understood that only one of the units in aradio set need have these elements. All of the selector cam assembliesin the various units, however. must rotate in proper synchronization andregistration with the selector switch 62, and this is accomplished byappropriate gearing and by the use of the singletooth ratchets. It willbe noted that there is no slip-clutch in the drive for the selector camarrangement; and accordingly, the driving elements of the single-toothratchets 36 in all of the various tuning units rotate in fixed relationto each other. Since the ratchets are of the single-tooth variety thissynchronization of the driving elements automatically results insynchronization of the driven elements, so that all of the variousselector cam arrangements upon the initiation of each tuning cycleassume a synchronized relation with each other and then rotate togetheruntil they are stopped to make corresponding selections of stopcombinations in all of the various tuning units. The lost motionconnection comprising the parts 60 and 6I is used to enable the selectorcams 38 to back off or shift position slightly as the portion 41a of thepawl drops into the selector cam slot. This movement of the selectorcams must be permitted without movement of the selector switch 62, sinceany movement of the rotatable portion of this switch which would causethe edges of its slot to again con-tact the switch point 63a would causeundesired disturbance of the cycle ofoperations.

The provision of a manual selector cam 39 and cooperating pawl 48.prevent any accidental and undesired operation of one of the tuningstop combinations when it is desired to manually tune the shaft. Whenmanual tuning is selected, movement of the portion 48a into the slot 39alocks the selector arrangement against rotation, so that vibration willnot accidentally bring a tuning stop combination into operation. Whenthe manual arrangement is actuated there is no hindrance to manualrotation of the shaft 24 as there is no projection on the outer end 48eof the manual pawl, and it cooperates with a smooth ring 28.

Referring now more particularly to the structural arrangement asillustrated in Figures 5 8, it will be seen that the parts are mountedin a self-contained unit between the plates 65 and 66 held in properrelation to each other by posts 61. A tuned shaft 24 carries anappropriate number (as I I) tuning stop rings 21A- K and the terminalstop ring 29, these being separated by spacer rings 69 keyed to a drumon the tuning shaft. Means is provided for selectively locking orunlocking the tuning stop rings 21 on the shaft 24 (not shown in detailhere), this means being operated by the manually rotatable operating barHa in the dial 10. Unlocking is only for the purpose of setting thetuning stop rings to a desired position, and operatively they act asthough they were at all times rigidly mounted on the shaft 24.

The secondary cams 42a-k are mounted on an appropriate drum on the shaft4 I, with operating rings between them. the arrangement beingsimisecondary cam shaftii. isgeared-to the main shaft 24 any change inthe setting of this latter eects a similarsetting of whichever secondarycam is in engagement with a stop pawl at that time.

Referring lnow more particularly to Figure 6,. it will be seen that theslip clutch 32 comprises as its two friction parts an annular shoe 02a'oi' non-metallic material (as fiber or plastic) encircling a metal drum32h ilxedly mounted on the shaft 24. The annular shoe is held in placewith the desired amount of frictional engagement by the encircling bandspring 32e. The worin gear 8|, rotatable about but not connected to theshaft 24, carries a stud 32d lying between the two end faces of the shoe32a, the operation preferably providing a little clearance or lostmotion. Rotation of the worm gear 3| by the worm 30 therefore transmitsits force to the shaft 24 by pressure against one or the other of theend faces of the friction shoe 32a; and when the frictional grip of theshoe 32h is exceeded, the worm gear 3| can rotate without rotation ofthe shaft 34, slippage taking place between the shoe and the drum. i

The details of the single-tooth ratchet are best seen in Figure 8. Thedriving element 30a is fixed to the worm gear 35, both being freelyrotated about the shaft 31; while the driven member 36h is xed to thisshaf-t so that movement of the driven member eects movement of theselector cam shaft 31. The driving member 38a is providedv with anannular slot 36e having a fixed (pin 36d in one portion thereof, thispin having a sloping face. The cooperating driven member is providedwith a bore or opening 38e in which a pin 36] is longitudinally movableagainst the force of a spring 36g, the bore registering with the annularslot. Rotation of the driving member in one direction (its direction ofrotation during the tuning portion of the cycle) brings the sloping faceinto engagement with the movable pin and does not effect rotation of thedriven shaft; rotation in the other direction (when the parts are beingdriven toward home position), however, causes driving engagement betweenthe pins and rotation of the selector drum and cams.

Before describing the limit switch in detail the general operation ofthe device will be described, with particular reference to the circuitdiagram, Figure ll. A battery is illustrated as representative of anyappropriate source of power for the motor and relays. The motor controlrelay |02 has an actuating coil |02a, three movable switch membersIDZb-d, three "upper contacts |02e-g, and three lower contacts |02h-j.This motor control relay and the limit switch 33 cooperate to achievethe desired sequence of operations.

A manual selector switch, here identified in general as |03, is shown ashaving I2 switch taps i a-l wired `to the corresponding switch points 63a-Z of the automatic selector switch, the manual switch arm |03m being'adapted to engage any one of the i2 switch points and thus to complete acircuit to any one of the correspending automatic selector switch taps.The switch |04 is shown in a position enabling control by this manualselector switch; but when the switch |06 is thrown to its other contacta control switch of any desired type at some remote point may beoperated. A relay has cooperating contacts |05c and |05e which controlthe tuning circuit, and other contacts which may assumo control carrieremission or any other desired circuit, this and the manual switch |08providing an interlocked action so that traon is not effected while theautomatic tuning/device is operated.

Assuming that the parts are as shown in Figures 5-8, and it is desiredto select another frequency setting, movement of the switch arm 103mmight be made to the contact |03lc, vas shown in dotted line position.This movement completes a circuit from ground through disk 82a, contact63k, wire |01, contact |03k, arm |03ml wire |08, switch |04, relay |08(it being assumed` that the carrier control switch |06 is open and thecoil |05a not energized), wire |00, motor relay coil I02a, wire H0,battery |0| and wire |I| to ground. This energizes the motor controlrelay and causes its movable switch elements |02b-d to move from thepositions shown to their lower positions. This energizes the motor 20 bya circuit including wire H0, contacts |02c and |021, the motor armature,

i, contacts |0212 and |0211., and wire back to the battery. This effectsrotation of the motor in the home direction. the ratchet backing up theselector cam drum and lifting the pawis 41h out of the secondary cam andstop ring slots. At the same time the actuating member 82 of the limitswitch 33 begins to travel downward and contact 33 makes engagement withthe contact 84, breaking its contact with 85 and disabling the carriercontrol switch |06 until the tuning cycle is completed. The disk 62a ofthe automatic selector switch is also rotating during this operation butintermittent breaking of the contacts 63k has no eiect because a holdingcircuit for the motor control relay has been energized through the limitswitch contacts 86 and 8l and relay contacts |0211 and |02j.

I'he motor continues operation until the tuned shaft has reached homeposition, the clutch thereafter slipping until the actuating member 82of the limit switch opens the holding circuit contacts 8S and 81. Thisreturns control to the automatic selector switch t2, and as soon as itreaches a position with its slot opposite the contact 03k the motorcontrol relay circuit is deenergized and the motor reverses, leaving theselector cams in a position corresponding to the selector tap 63k,rendering a desired stop combination operable. l

Return of the movable parts of the motor control relay to the positionshown in the drawings completes another circuitto the motor in such away as to cause its operation in a reverse direction, as mentioned, thiscircuit including wire i0, contacts |020 and |02f, wire H2, contacts 03and 00, wire H3, contacts |021) and |026, the motor armature, contacts|02d and |029, and Wire back to the battery, it being noted that theupper end of the battery is now connected to the lower end of thearmature, the reverse of the previous case. This causes movement of thevarious tuning device partsfin the tuning direction, this continuinguntil the tuning shaft is stopped in its appropriate position byengagement of the chosen pawl with the forward shoulder of itscooperating stop ring slot (as illustrated in Figures 4 and 7), theclutch thereafter slipping to permit the motor drive to continue toterminal position. This terminal position is determined by opening ofthe limit switch contacts 83 and 84 by the actuating member 82. Abridging resistor Ht is associated with these contacts to always providejust enough current to keep the pawl in firm enf sagement with theshoulder of its cooperating stop split, the two split 92 threaded into astud 94a.'

`ing with respect to to overcome the limit switch should havecorresponding rotation.

In order to enable this to be accomplished within reasonable limitationof space and with a. good degree of accuracy the rotatable portion ofthe limit switch is made inthe form of a threaded shaft member 8i. Asmay be best seen in Figures and 7, the shaft 8l is geared to the drivingelement of the clutch 32 by gears 8B and 89 of equal size (the gears 3|and 8.9 being rigidly fastened together), so that rotation oi' the shaftsi always corresponds exactly to that of the line shaft.

is may be best seen inFigures 9 and'lO, enlarged views, the shaft di hasthreaded thereon a nut all with a cylindrical bearing portion Qta onwhich the actuating member 82 is/rotatably mounted for frictiona'lengagement therewith, the parts being heldin desired relation by theiianges 99h and 90o on the nut. As may be best seen in Figure 7, theactuating member 82 is centrally portions 82a and 82h being urgedtogether by the force of a spring iii, this being readily adjustable byrotation of the stud cooperating sleeve 92a in the portion 82h oi theactuating member. The outer ende of the actuating member are providedwith a semi-circular groove or depression embracing the post @la topermit axial but prevent rotationai movement 'ofthe actuating member.

Thev cycle of operations of the tuning device, particularly at the homeend where the selector cams must be positioned, requires that the tuningshaft (and thus the threaded shaft iii of the limit switch) rotate afterthe actuating member has reached its home terminal position (shown indotted lines in Figure 9) and opened the contacts tt and til; and thereis a certain amount of overrun at the other terminal position (shown insolid lines). In order to stop the actuating member, Without jamming orsticking of the threaded shaft 8|, I have provided the slipclutcharrangement between the nut 99 and the actuating member 32 aspreviously described, and means for positively rotating the nut withinthe actuating member.

In order to eiiect this rotation, collars 93 and 94 are rigidly mountedon the threaded shaft at site direction, the

' tively rotated each end thereof, the collar 93 having a projectingshoulder portion or stud 93a and the collar 94 having a similarprojection shoulder portion or The nut is provided with cooperatingshoulder portions on each side comprising the f' studs 90d and 90e. Ifthe parts be assumed to be in the positions shown in solid lines inFigure 9, at the beginning of a tuning cycle, initiation of the tuningoperation by movement of the manual switch arm ||l3m starts the threadedshaft 9| rotating in a counter-clockwise direction (speak- Figure 10) inexact correspondence with the rotation of the driving elementof theclutch 32. Since the studs 94a and 90e are in the relation shown inFigure 10, the stud 94a can move away (counter-clockwise) with nofrictional resistance of any kind to suchmovement: and the actuatingmember 82 starts to move along the shaft to the left (as shown in Figure9), the friction al engagement between it and the nut preventingrotation between these two parts. As the actuating member moves to theleft, its motion '1, wherein the last e'ects a change in therelationship of the contacts 83, 34 and 8B, as previously described;then moves through the desired period of drive motion (slightly morethan twenty turns in the unit illustrated); and finally strikes contact86 and'opens its engagement with contact 8l. Just after this has beendone the moving parts reach the position shown in dotted lines in Figure9 and stud 93a comes into contact with stud 90d, in a squared andnon-wedging engagement of the same kind illustrated in Figure 10. Thisengagement causes rotation of the nut within the actuating member, thislatter member slipping on the bearing surface Qta. Yet despite the forcerequired to cause this slip-clutch action, the studs 93a and 90d are insuch relation that whenthe motor reverses and the threaded shaft 8istarts to rotate in the oppoactuating member and nut may start to moveback to their initial position with no i'rictional resistance orhindrance to the starting of such movement. That is, while the nut isposieach end of the travel of the latter, this positive rotating meansdoes not wedge or jam in any way and the parts release instantly andmove back in the other direction upon within forces Well within thatprovided by the slip-clutch frictional engagement.

While I have shown and described certain embodiments of my invention, itis to be understood that it is capable oi many modifications. Changes,therefore, in the construction and arrangement may be made withoutdeparting from the lspirit and scope of the invention as disclosed inthe appended I claim:

i. In Aautomatic tuning apparatus for positioning a rotatable shaft,including reversible drive means adapted to rotate the shaft through apiurality of revolutions, a slip clutch in the connecclaims.

tion between the drive means and the shaft, a

plurality of stopping to stop the shaft at where in its range means,each being adapted a predetermined point anyof rotation, and selectingmeans for rendering operative a desired one of said stop means, thisselecting means including a rotatable selector switch, a limit switchincluding: a threaded shaft member; switch means adjacent at least oneend of the threaded member; a nut on said shaft; an actuating member'rotatably mounted on said nut and having appreciable frictionalengagement therewith, one of said members being adapted tobe rotated byand in accordance with rotation of the drive means, movement of theactuating member along the threaded shaft being adapted to operate theswitch means; and means for causing the nut to rotate with the threadedshaft at the desired limits of movement of the actuating member.

2. Apparatus of the character claimed in claim 1, wherein the lastmentioned means includes shoulder means on the nut and cooperatingshoulder means rigidly mounted on the threaded shaft.

3. Apparatus of the character claimed in claim mentioned means includesshoulder means on each side of the nut and cooperating shoulder meansrigidly mounted on the threaded shaft at each end thereof.

4. In automatic tuning apparatus for positioning a rotatable shaft,including reversible drive means adapted to rotate the shaft through aplurality oi revolutions, a slip clutch in the connection between thedrive means and the shaft, a plurality of stopping means, each beingadapted within the actuating member at reversal of the motor a rotatableselector switch, a limit switch in' cluding: a threaded shaft memberadapted to be rotated by and in accordance with rotation of the drivemeans; switch means adjacent each end of the threaded shaft; a nut onsaid shaft;

an actuating member rotatably mounted on saicly nut and havingappreciable frictional engagement therewith; means preventing rotationalbut permitting axial movement; of the actuating esonero threaded shaftmember; a nut on said shaft; an actuating member rotatably mounted onsaid nut and having appreciable frictional engagement therewith, one ofsaid members being adapted to be rotated through a plurality ofrevolutions, movement of the actuating member alongthe threaded shaftbeing adapted to operate the movable element; shoulder means on the nutproviding a shoulder surface parallel to the axis of the member,movement of the actuating member along the threaded shaft being adaptedto operate the switch means; shoulder means on each side of the nut; andcooperating shoulder means rigidly mounted on the threaded shaft at eachend thereof, wherebyY the nut is caused to rotate with the threadedshaft, but without jamming thereon, at the desired limits of movement ofthe actuating member.

5. Apparatus of the characterclaimed in claim l, whereinthe actuatingmember includes means for readily adjusting said frictional engagement.

6. Apparatus of the character claimed in claim) 4, wherein the actuatingmember includes means for readily adjusting said frictional engagement.-

7. Apparatus of the character claimed in claim l, wherein the nut hasannular flanges on each side thereof and the actuating member isrotatably mounted therebetween.

8. Apparatus of the character claimed in claim 4, wherein the switchmeans at one end. of the shaft comprises a single pair of contacts andtho switch means at the other end of the shaft provides -two pair ofAoppositely operating contacts,

one pair closing when the other opens and vice versa.

9. Apparatus of the character described for actuating' a movablevelement, including: e

shaft; and cooperating shoulder means rigidly mounted on the threadedshaft providing a shoulder surface parallel to the axis of the shaft,whereby the nut is caused to rotate with the threaded shaft, but withoutjamming thereon, at the desired limits of movement of the actuatingmember. 5

10. Apparatus of the character. described for actuating a limit switch,including: a threaded shaft member adapted to be rotated through aplurality of revolutions; a nut on said shaft; an

actuating member rotatably mounted on said nut and having appreciablefrictional engagement therewith: means preventing rotational butpermitting axial movement of the actuating member, movement of theactuating member along the threaded shaft being adapted to operate theswitch means; shoulder means on each side of the nut providing shouldersurfaces parallel to the airis,v of the shaft; and cooperating shouldermeans rigidly mounted on the threaded shaft at each end thereofproviding shoulder surfaces parallel to the axis of the shaft, wherebythe nut is caused to rotate with the threaded shaft, but without jammingthereon, at the desired limits of movement of the actuating member.

11. Apparatus of the character claimed in claim 9, wherein the actuatingmember includes means for readily adjusting said frictional engagement.

RICHARD W. MAY.

